Chronologies of Contaminant Input to the Hudson River Estuary

How can sediment cores be used to evaluate contaminant input and deposition in the Hudson River system? First and foremost is the requirement of finding a site where deposition is rapid and a long (at least multidecadal) record is preserved. Such sites offer the opportunity to determine trends in contaminant input as well as to assess the relative importance of multiple sources. As noted above, the Hudson has such sites and cores can be dated using a variety of natural and anthropogenic radionuclides. In a study fo-cussed on characterizing contaminant histories in the Hudson, Richard Bopp and James Simpson of Lamont-Doherty Earth Observatory used 137Cs, Pu isotopes, 60Co and 7Be to date a suite of cores collected at key locations in the upper and lower Hudson from 1975 to 1986 (Bopp and Simpson, 1989; see Chapter 26 in this volume for further information). Several types of contaminants were measured:

• Polychlorinated Biphenyls (PCBs) - These organic compounds are noted for their insulating properties and have been released to the Hudson from a variety of sources. A principal source up-river has been the inputs from capacitor plants operated by the General Electric Company. PCBs that have been used commercially contain mixtures of nearly identical compounds (termed congeners) that differ in the number and arrangement of chlorine atoms. The cores analyzed by Bopp and Simpson (1989) show peaks in PCB deposition in the early to mid-1970s that were attributed to the removal of a dam in 1973. PCB-contaminated sediments were transported downriver following removal of the dam. Although the maximum PCB concentration occurs in cores throughout the estuary at about the same date, the PCB concentrations decrease from high values upriver to lower values in New York Harbor. The mix of PCB congeners in the latter sediments suggests both a source from upriver and from the New York metropolitan area. As the PCB-contaminated sediments have been buried, the upriver sources have become progressively less important in supplying these contaminants to the lower estuary. More recent profiles of PCB concentrations in Hudson sediments were examined by Steven Chillrud as part of his doctoral work at Columbia University (Chillrud, 1996). These results show continuing decreases in sediment PCB concentration through the 1980s (Bopp and Simpson, 1989; Chillrud, 1996).

• Pesticides - Bopp and Simpson (1989) also measured the chronologies of accumulation of the chlorinated hydrocarbon pesticides DDT and chlordane in Hudson sediments. In the cases of these contaminants, the New York metropolitan area is the dominant source, and the downriver increases in concentrations reflect this fact. The accumulation of both pesticides peaked in the 1970s, consistent with the timing of bans in their use (1972 for DDT; 1975 for chlordane).

• Concentrations of the trace metals copper and lead showed some declines in the cores studied by Bopp and Simpson (1989), but not to the extent that might be expected from efforts to reduce the concentrations of these metals in wastewater entering the system. A similar decline in zinc concentrations since the 1970s also was documented by Chillrud (1996). Lead has both significant atmospheric and watershed sources to coastal waters in New York (Cochran et al., 1998; Chillrud et al., 1999), although the decrease in the use of leaded gasoline has diminished the atmospheric source of this heavy metal. It is possible that continuing inputs of trace metals from the Hudson River watershed have moderated declines in input from urban point sources.